Over a century ago, a man named Wilhelm von Pittler filed a patent application for a gear manufacturing process called power skiving. This was a revolutionary idea back in 1910. However it is only recently, with the advent of modern manufacturing, that it has become more widely adopted now that machining centres are equipped with systems for controlling and synchronising the spindle speed and with process optimisation software. It is only because of these systems that this extremely complex technology can be used. Collins Aerospace, based in Figeac (France), has been relying on this highly productive technique since 2019. Machine operator Jean-Paul Noyes, team leader Jean Pierre Destruel, process engineer Joel Bousquet and process developer Pascal Moulènes (the company’s specialist for gear-related matters) teamed up with tool partner HORN to implement the gear skiving process for various types of part.

“Lots of companies can sell, but it’s rare to find one that can develop manufacturing strategies and actively support the implementation process”, says Pascal Moulènes regarding the introduction of the gear skiving process. He then adds: “In 2015, we saw this process being used by a machine tool manufacturer to mass-produce machine tool components.” This got the key people at Collins interested in how they could use it themselves and influenced their decisions when selecting new machining processes. After investing in modern machining centres capable of supporting the technology, Pascal Moulènes and his team started looking for a supplier of gear skiving tools.

“At EMO 2017 in Hannover, we witnessed the process in action on the HORN stand and – given that we were already on the lookout for a new supplier of carbide gear skiving tools – we were very interested indeed”, explains Moulènes. Technical support for the project was provided by engineer Emmanuel Gervais. He is the primary contact at HORN when it comes to machining critical aerospace components and he also supports the development of new tool concepts by providing valuable expertise and experience. Unsurprisingly, Gervais is based in the area of south-west France around Toulouse – the epicentre of the European aerospace industry.

Prior to the introduction of the gear skiving process, the components were being manufactured with conventional cutting tools. “We were in the process of reorganising the production of our families of gears”, explains Pascal Moulènes. With the help of the new technology, Moulènes was able to optimise the production processes because fewer set-up operations were required and he also managed to eliminate the idle time between work steps. In addition to reducing cycle times, the technology also increased component quality.

A new process

“The gear skiving process was new to Collins and so we had to start by getting to know it in detail. However, we were not in a position to carry out any lengthy test runs because of the sheer volume of orders”, clarifies Moulènes. Gervais therefore suggested carrying out the tests at the HORN test centre in Tübingen. “The optimum machining parameters for 16NCD13 (1.6657), a material that is relatively difficult to machine, were determined in Tübingen following multiple test series. The results were reproducible across all products and the quality was consistently high”, he says. HORN sent the test parts back to the Collins plant so the quality could be checked. The maximum permissible profile error for the gear teeth is a deviation of 0.03 mm (0.001"). The average deviation for the HORN test series was significantly lower than this. “HORN was able to supply the gear skiving tools with a concentricity correction system. Naturally, our primary aim was to achieve the appropriate level of part quality, but a long tool life was also very important to us”, adds machine operator Joel Bousquet.

The introduction of the gear skiving process at Collins went without a hitch: “The initial tests proved immediately successful. We were able to take the cutting data that had been determined for the process in Tübingen and apply it with virtually no changes”, asserts Emmanuel Gervais. The machining time for the gear teeth alone was cut by more than half. The gear skiving process is subdivided into 14 rough machining, 2 pre-finishing and 2 finishing operations with a grinding allowance of 0.1 mm (0.004"). The hardening distortion associated with the subsequent heat treatment is not factored into the cutting profile of the tool. After hardening, the component then has to be ground.  “We are currently using the same tool to manufacture five different components with the same module. So far, we have produced more than 300 parts in total. And the end of the tool life is not yet in sight”, says Pascal Moulènes.

Productive tool system

The HORN tool range includes highly productive gear skiving tools for manufacturing internal gears, splines and other internal profiles, as well as external gears with interfering edges. In these applications, the key advantages offered by gear skiving are: significantly shorter process times compared to broaching, the ability to use the technique on optimised turn-mill centres, turning and gear cutting in one clamping, and the absence of reliefs at the tooth end. Gear skiving tools are designed for gear cutting in medium to large batches. Each tool is individually adapted to the application and to the material being machined, with the various tool interfaces based on the number of teeth and the module.

HORN’s gear cutting portfolio comprises a wide range of tools for the production of various gear geometries with module 0.25 to module 30. Whether this involves teeth for spur gears, shaft/hub connections, worm shafts, bevel gears, pinions or customised profiles, all these tooth profiles can be manufactured cost-effectively with HORN tool solutions. Gear skiving technology only came into use when machining centres started supporting the use of this complex technology by offering systems for controlling and synchronising the spindle speed, as well as process optimisation software.

A global company

With more than 70,000 employees based at 300 locations across the globe, Collins Aerospace is one of the biggest suppliers to the aerospace industry. Its customer base includes all of the major international corporations in this sector. The Collins plant in Figeac is one of the world’s leading manufacturers of propeller systems for civil and military aircraft, of cockpit and cabin equipment, and of horizontal tail actuators. At its plant in the south of France, it also manufactures the propellers for the Airbus A400M.

Collins Aerospace and HORN have been partners for 30 years. “It all began when we started using the Mini and Supermini systems to machine Inconel”, recalls Pascal Janot, who is in charge of tool procurement. Today, the team at Collins also uses HORN solutions for milling in addition to the Mini and Supermini systems. “Our company relies on HORN for the majority of parts where we need to cut grooves. But HORN does not just offer excellent tools. Thanks to its high-quality support and services, the company is our preferred partner”, says Pascal Moulènes.